Two novel laser absorption diagnostics for allene and propyne are presented. Through examination of the high temperature spectra of the two C3H4 isomers via two fast-wavelength-scanning, broadband ...external cavity quantum cascade lasers, 1930.38 cm−1 and 1233.3 cm−1 were chosen as the wavelengths for a two-species, two-wavelength diagnostic pair that minimizes interference from other species. Absorption cross sections for allene and propyne were measured at each of these wavelengths over 1196–1502 K, at 1.3–1.6 atm. Once characterized, these diagnostics were employed to measure the mutual isomerization rates of allene and propyne over the same temperature range. The two rates are reported as kA->P (1202–1502 K) = 2.64 × 1012exp(-59,214/RT) ±14% and kP->A (1196–1494 K) = (4.19 × 1012)exp(-61,912/RT) ±17%. These rates were found to be in excellent agreement with limited past experimental determinations and recently computed rates. Using these rates, the equilibrium constant is also reported as a function of temperature.
In this work, we investigated the self-reaction of allyl radicals and its cross-reaction with hydroxyl radical by employing shock tube and laser absorption techniques. We carried out the experiments ...behind reflected shock waves over the temperature range of 800–1200 K and pressures of 1.1–2.5 bar. We generated allyl (C3H5) and OH radicals by fast thermal decomposition of allyl iodide (C3H5I) and tert-butyl hydroperoxide (TBHP), respectively, and monitored reaction progress by detecting OH near 306.69 nm and C3H5 near 220 nm using UV laser absorption. At the detection wavelength, we measured the temperature dependence of the absorption cross-sections of C3H5 and C3H5I. Rate coefficient for the self-recombination reaction of allyl radicals showed a small negative temperature dependence and no noticeable fall-off behavior over 1.15–1.96 bar giving a mean value of kC3H5+C3H5=(1.0±0.2)×10−11cm3molecule−1s−1. Likewise, the cross-reaction of allyl and OH radicals did not exhibit discernible pressure and temperature dependence under our experimental conditions indicating a barrierless reaction, and an average value of kC3H5+OH=(9.3±0.7)×10−11cm3molecule−1s−1 best illustrates our measured rate coefficients. These measurements represent the first direct experimental determinations of the rate coefficients for these important radical-radical reactions at high temperatures and pressures.
Generation of vortex beams with tunable topological charges is of significant importance in a wide range of applications. A novel method is proposed to generate such donut-like Laguerre–Gaussian (LG) ...vortex beam by the solid-state zigzag tube lasers. The LG TEM0l mode with tunable beam order l can be directly obtained from the tube laser oscillator by simply adjusting a mode selector consisting of a pair of complementary cone lenses and an amplitude mask. Subsequently, the LG beam with topological charge of +l or −l is constructed by the coherent superposition of the LG TEM0l modes with appropriate phase difference. This method enables the generation of LG beams with high mode purity, and the value and sign of the topological charges of the generated LG beam can be individually and flexibly controlled by appropriately adjusting the mode selector and the phase difference of LG TEM0l modes, respectively. The physical model of the method was established, and the feasibility for generating topological-charge-tunable LG0l beams was demonstrated by numerical simulation. All the generated LG0l beams possess high purities and the highest purity reaches to 99.3% in the simulation. This method provides an alternative approach to generate topological-charge-tunable LG beam in solid-state lasers.
This paper evaluates three critical plane criteria, namely the Findley, Matake and modified Wöhler curve method and compares them to the IIW’s implementation of the Gough–Pollard criteria. Assessment ...is conducted on a large set of fatigue data of thin-walled tube–tube laser beam welded specimens made of magnesium and aluminum alloys that were tested under proportional/non-proportional and constant/variable amplitude loading. Each criterion is evaluated based on their assessment reliability using both design and experimental S-N curves. The critical plane approaches show encouraging results for weld fatigue assessment but lead to non-conservative fatigue assessment in comparison to the IIW’s Gough–Pollard criteria.
•Multiaxial variable amplitude fatigue of thin welded specimens.•Comparison of multiaxial fatigue criteria.•Notch stress approach applied to welded joint fatigue.•IIW predicts conservative fatigue life estimations.
The speciation of jet-fuel pyrolysis plays an important role in the development of predictive models for jet-fuel combustion. In this work, a multi-wavelength speciation technique was applied to a ...large dataset of shock-tube laser-absorption measurements of jet-fuel pyrolysis. A novel absorbance model was developed to interpret the measurements at common conditions, and pyrolysis product time-histories and early-time yields are reported for three jet fuels at five high-temperature conditions. Specifically, methane, ethylene, and lumped vinyl-group time-histories, in addition to aromatics (benzene and toluene) yields, were quantified using eight wavelengths over conditions 1040–1480 K, 1–3 atm, for jet fuels JP8, Jet-A, and JP5. Results are presented at 1150 K, 1200 K, 1250 K, 1300 K, and 1350 K. Additional relationships between vinyl-group-containing species, namely propene, 1-butene, and 1,3-butadiene, are explored. The mole fraction time-histories exhibit good agreement with the literature and extend the speciation of these jet fuels to the limits of current spectroscopic techniques.
Laser forming is one of the most recent forming processes developed which uses a laser beam to induce a deliberate thermal stress on a workpiece to form a sheet metal. Accordingly, bending tubes ...using laser beam have attracted the attention of many engineers. In this paper, we studied the effects of various laser beam parameters on the tube bending process. To investigate the effects of all the parameters, we performed a large number of analyses and generated applicable tube laser bending data. We utilized Taguchi design of experiment method to manage the finite element simulation of the laser forming process. Subsequently, to have an easier, but more flexible and more complete laser forming data bank, we employed artificial neural networks to predict the required tube bending parameters for the proposed forming criteria. Finally, we used genetic algorithm programming to solve the multi-objective optimization with respect to the laser forming parameters. The objectives include maximum bending angle, minimum ovality, minimum thickening, and minimum forming energy consumption. The results from this study indicate that we can use applied data tables to find the optimum tube laser forming parameters. The outcome of the numerical experiments is consistent with the existing literature on the laser forming process.
This study demonstrates controllable random lasing emissions in a dye-doped nematic liquid crystal (DDNLC)-infiltrated microcapillary. The emission wavelength of the micro tube laser can be adjusted ...by changing the focusing position of the pumped pulses on the center or the periphery of the liquid crystal region of the microcapillary. In addition, with doping azo-dyes in the DDNLC of the micro tube laser, optical controllability of the lasing intensity and wavelength can be further achieved. The controllable micro tube laser may find highly widespread photonic applications in multicolor emitting sources, and vibration and UV sensors.
All-solid-state tube lasers (ASSTLs) with zigzag beam path combine the attractive properties of rod, slab, and disk lasers. However, the analysis on the beam quality of tube lasers is rarely ...reported. In order to explore how and how seriously the static errors including fabricating and alignment errors degrade the beam quality of a tube laser, a theoretical model of a nonideal ASSTLs constructed in master oscillator power amplifier (MOPA) configuration has been built up by taking the static errors into consideration. On the basis, the influence of the fabricating and alignment errors on the static beam quality of the ASSTLs was analyzed in detail, and the annular aberration of the output beam was discussed as well. Simulation results indicate that the static beam quality of tube lasers strongly depends on the fabricating and alignment errors. These static errors would severely degrade the output beam quality of the ASSTLs and even result in coma and defocus aberrations. This work may provide valuable references for the design, processing, and applications of ASSTLs.
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